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Caption

Thin film interference on soap film. Bands of colour are created by white light shining on a film of soap. Some of the light reflects off the surface of the film, while the rest of the light travels through the film and reflects off the back of the film. The reflected light waves interfere with each other, either constructively (coloured bands) or destructively (black bands). Different colours are seen due to varying film thickness and viewing angles. If the soap film is held vertically (seen here), the film will be thicker at the bottom, creating a high gradient of thickness in relation to height and making the bands of colour thinner.